Field of the Invention
The invention concerns an arrangement for the actuation of at least one element in an optical system.
The arrangement according to the invention can be used advantageously in particular in optical systems with a plurality of elements (for example optical elements) that are adjustable independently of one another, for example for the actuation of a facet mirror in a microlithographic projection exposure apparatus. However, the invention is not restricted to this, but can also be used generally in other optical systems (for example optical systems for the working of materials), and in particular systems in which a plurality of elements are respectively mounted adjustably in a confined installation space.
Prior Art
Microlithography is used for the production of microstructured components, such as for example integrated circuits or LCDs. The microlithographic process is carried out in what is known as a projection exposure apparatus, which has an illumination device and a projection lens. The image of a mask (=reticle) illuminated via the illumination device is thereby projected via the projection lens onto a substrate (for example a silicon wafer) that is coated with a light-sensitive layer (photoresist) and is arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
In a projection exposure apparatus designed for EUV (i.e. for electromagnetic radiation with a wavelength below 15 nm), mirrors are used as optical components for the imaging process because of the lack of light-transmissive materials. Furthermore, in particular in the illumination device of a microlithographic projection exposure apparatus designed for operation in EUV, the use of facet mirrors in the form of field facet mirrors and pupil facet mirrors as bundle-guiding components is known, for example from DE 10 2008 009 600 A1. Such facet mirrors are made up of a multiplicity of individual mirrors that are respectively designed to be tiltable via flexures for the purpose of adjustment or for realizing certain distributions of the illumination angle. At the same time, there is also a need to realize tilting about two tilting axes (in particular perpendicular to one another).
A problem that arises here in practice is that, for actuating the individual mirrors of a facet mirror for instance (or other elements in arrangements in which these elements are comparatively closely packed), only a confined installation space is available. In this space it is necessary on the one hand to realize joints that flex as much as possible—in order to minimize the forces on the actuator—and on the other hand often also to dissipate thermal loads acting on the facet—for instance during operation of the projection exposure apparatus. In particular in applications in which comparatively large tilting angles (in the case of the individual mirrors of a facet mirror for example of over 30 mrad) are to be realized, the aforementioned boundary conditions present demanding challenges for the design of the joints. In this respect, the limited installation space in the case of a facet mirror for instance presents a problem to the extent that, when actuating the individual mirrors, it is intended to avoid their rotation about the mirror axis (perpendicular to the respective mirror plane) and an accompanying collision of the individual mirrors, generally via additional measures in the structural design.
As prior art, reference is made, only by way of example, to DE 199 05 779 A1 and DE 10 2009 044 957 A1.